Last updated October 9, 2018 The structure of Chariklo's rings from stellar occultations D. B´erard1, B. Sicardy1, J. I. B. Camargo24;25, J. Desmars1, F. Braga-Ribas27;24;25, J.-L. Ortiz3, R. Duffard3, N. Morales3, E. Meza1, R. Leiva1;6, G. Benedetti-Rossi24;25, R. Vieira-Martins4;23;24;25, A.-R. Gomes J´unior23, M. Assafin23, F. Colas4, J.-L. Dauvergne41, P. Kervella1;26, J. Lecacheux1, L. Maquet4, F. Vachier4, S. Renner51, B. Monard52, A. A. Sickafoose35;36, H. Breytenbach35;49, A. Genade35;49 1 W. Beisker10;44, K.-L. Bath10;44, H.-J. Bode10;44;, M. Backes50 V. D. Ivanov14;15, E. Jehin5, M. Gillon5 J. Manfroid5 J. Pollock7, G. Tancredi20, S. Roland19, R. Salvo19, L. Vanzi2, D. Herald11;12;18, D. Gault11;17, S. Kerr11;28, H. Pavlov11;12, K. M. Hill29, J. Bradshaw12;13, M. A. Barry11;30, A. Cool33;34, B. Lade32;33;34, A. Cole29, J. Broughton11, J. Newman18, R. Horvat17, D. Maybour31, D. Giles17;31, L. Davis17, R.A. Paton17, B. Loader11;12, A. Pennell11;48, P.-D. Jaquiery47;48, S. Brillant15, F. Selman15, C. Dumas53, C. Herrera15, G. Carraro43, L. Monaco40, A. Maury21, A. Peyrot42, J.-P. Teng-Chuen-Yu42, 46 37 arXiv:1706.00207v2 [astro-ph.EP] 18 Sep 2017 A. Richichi , P. Irawati , C. De Witt10, P. Schoenau10, R. Prager44, C. Colazo8;9, R. Melia9, J. Spagnotto22, A. Blain39, S. Alonso16, A. Rom´an38, P. Santos-Sanz3, J.-L. Rizos3, J.-L. Maestre45, D. Dunham12 { 2 { 1 LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universit´es, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cit´e 2 Department of Electrical Engineering and Center of Astro-Engineering, Pontificia Universidad Cat´olica de Chile, Av. Vicu~naMackenna 4860, Santiago, Chile 3Instituto de Astrof´ısica de Andaluc´ıa,CSIC, Apt. 3004,18080 Granada, Spain 4IMCCE, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universits, UPMC Univ. Paris 06, 77 av. Denfert-Rochereau, 75014, Paris, France 5Institut d'Astrophysique de l'Universit´ede Li`ege,All´eedu 6 Ao^ut17, B-4000 Li`ege, Belgique 6Instituto de Astrof´ısica, Facultad de F´ısica, Pontificia Universidad Cat´olica de Chile, Av. Vicu~naMackenna 4860, Santiago, Chile 7Physics and Astronomy Department, Appalachian State Univ., Boone, NC 28608, USA 8Ministerio de Educaci´onde la Provincia de C´ordoba, C´ordoba, Argentina 9Observatorio Astron´omico, Universidad Nacional de C´ordoba, C´ordoba, Argentina 10IOTA/ES, Barthold-Knaust-Strasse 8, D-30459 Hannover, Germany 11Occultation Section of the Royal Astronomical Society of New Zealand (RASNZ), Wellington, New Zealand 12International Occultation Timing Association (IOTA), PO Box 7152, Kent, WA 98042, USA 13Samford Valley Observatory, QLD, Australia 14 ESO, Karl-Schwarzschild-Str. 2, 85748 Garching bei, M¨unchen,Germany 15ESO, Alonso de Cordova 3107, Casilla 19001, Santiago 19, Chile 16Software Engineering Department, University of Granada, Spain 17Western Sydney Amateur Astronomy Group (WSAAG), Sydney, NSW, Australia 18Canberra Astronomical Society, Canberra, ACT, Australia 19Observatorio Astron´omico Los Molinos, DICYT, MEC, Montevideo, Uruguay { 3 { 20Dpto. Astronomia, Facultat de Ciencias, Uruguay 21San Pedro de Atacama Celestial Explorations, Casilla 21, San Pedro de Atacama, Chile 22Observatorio El Catalejo, Santa Rosa, La Pampa, Argentina 23Observat´oriodo Valongo/UFRJ, Ladeira Pedro Antonio 43, RJ 20.080-090 Rio de Janeiro, Brazil 24Observat´orioNacional/MCTIC, R. General Jos´eCristino 77, RJ 20921-400 Rio de Janeiro, Brazil 25Laborat´orioInterinstitucional de e-Astronomia - LIneA, Rua Gal. Jos´eCristino 77, Rio de Janeiro- RJ 20921-400, Brazil 26Unidad Mixta Internacional Franco-Chilena de Astronom´ıa(CNRS UMI 3386), Departamento de Astronom´ıa,Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Chile 27Federal University of Technology- Paran´a(UTFPR/DAFIS), Rua Sete de Setembro, 3165, CEP 80230-901, Curitiba, PR, Brazil 28 Astronomical Association of Queensland, QLD, Australia 29School of Physical Sciences, University of Tasmania, Private Bag 37, Hobart, TAS 7001, Australia 30Electrical and Information Engineering Department, University of Sydney, Camperdown, NSW 2006, Australia 31Penrith Observatory, Western Sydney University, Sydney, NSW, Australia 32Stockport Observatory, Astronomical Society of South Australia, Stockport, SA, Australia 33Defence Science & Technology Group, Edinburgh, South Australia 34The Heights Observatory, Modbury Heights, South Australia 35South African Astronomical Observatory, PO Box 9, Observatory, 7935, South Africa 36Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology Cambridge, MA 02139-4307, United States 37National Astronomical Research Institute of Thailand, Siriphanich Building, Chiang Mai 50200 - Thailand { 4 { 38Sociedad Astron´omica Granadina, Granada, Spain 39Asociaci´onArgentina Amigos de la Astronom´ıa,Av. Patricias Argentinas 550, Buenos Aires, Argentina 40Departamento de Ciencias Fisicas, Universidad Andres Bello, Fernandez Concha 700, Santiago, Chile 41 Ciel & Espace, Paris, France 42 Makes Observatory,La R´eunion,France 43 Dipartimento di Fisica e Astronomia, Universita di Padova, Italy 44 Internationale Amateursternwarte e. V., IAS, Hakos/Namibia and Bichlerstr. 46, D-81479 M¨unchen(Munich), Germany. 45 Observatorio Astron´omico de Albox, Apt. 63, 04800 Albox (Almeria), Spain 46 INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy 47 Royal Astronomical Society of New Zealand (RASNZ), Wellington, New Zealand 48 Dunedin Astronomical Society, Dunedin, New Zealand 49 University of Cape Town, Department of Astronomy, Rondebosch , Cape Town, Western Cape, South Africa, 7700 50 Department of Physics, University of Namibia, 340 Mandume Ndemufayo Ave, P/Bag 13301, Windhoek, Namibia 51IMCCE, Observatoire de Paris, CNRS UMR 8028, Universit´eLille 1, Observatoire de Lille 1 impasse de l'Observatoire, 59000 Lille, France 52Kleinkaroo Observatory, Calitzdorp, St. Helena 1B, P.O. Box 281, 6660 Calitzdorp, Western Cape, South Africa 53TMT International Observatory, 100 West Walnut Street, Suite 300, Pasadena, CA 91124, USA { 5 { ABSTRACT Two narrow and dense rings (called C1R and C2R) were discovered around the Centaur object (10199) Chariklo during a stellar occultation observed on June 3, 2013 (Braga-Ribas et al. 2014). Following this discovery, we have planned observations of several occultations by Chariklo's system in order to better char- acterize the ring and main body physical properties. Here, we use 12 successful Chariklo's occultations observed between 2014 and 2016. They provide ring pro- files (physical width, opacity, edge structure) and constraints on their radii and pole position. Our new observations are currently consistent with the circular ring solution and pole position, to within the ±3:3 km formal uncertainty for the ring radii, derived by Braga-Ribas et al. (2014). The six resolved C1R profiles reveal significant width variations from ∼ 5.5 to 7 km. The width of the fainter ring C2R is less constrained, and may vary between 0.1 and 1 km. The inner and outer edges of C1R are consistent with infinitely sharp boundaries, with typical upper limits of one kilometer for the transition zone between the ring and empty space. No constraint on the sharpness of C2R's edges is available. A 1σ upper limit of ∼ 20 m is derived for the equivalent width of narrow (physical width < 4 km) rings up to distances of 12,000 km, counted in the ring plane. Subject headings: Rings - Centaur objects: individual (Chariklo) - Stellar Occul- tations 1. Introduction The asteroid-like body (10199) Chariklo is a Centaur object orbiting between Saturn and Uranus. It probably moved recently (∼ 10 Myr ago) from the Trans-Neptunian region to its present location, and will leave it on a similar short time scale, due to perturbations by Uranus (Horner et al. 2004). With a radius of 119 ± 5 km, estimated from thermal measurements (Fornasier et al. 2014), it is the largest Centaur known to date, but still remains very modest in size compared to the telluric or giant planets. On June 3, 2013, a ring system was discovered around this small object during a stellar occultation. Two dense and narrow rings, 2013C1R and 2013C2R (C1R and C2R for short) were detected. They are 1Deceased on 16 July 2017 { 6 { separated by about 15 km and orbit close to 400 km from Chariklo's center (see Braga-Ribas et al. (2014) for details). Until 2013, rings were only known around the giant planets. This discovery was thus surprising, and is a key to better understanding of the planetary rings, since they now appear to be more common than previously thought. In particular, the two rings being dense, narrow and (at least for C1R) sharp-edged, they look like several of the dense ringlets seen around Saturn and Uranus (Elliot and Nicholson 1984; French et al. 1991, 2016). In that context, there was a strong incentive for planning more occultation campaigns, first to unambiguously confirm the existence of Chariklo's rings and second, to obtain more information on their physical properties. While the discovery occultation of June 3, 2013 provided the general ring physical parameters (width, orientation, orbital radius, optical depth,...), several questions are still pending, some of them being addressed in this work: do the rings have inner structures that give clues about collisional processes? How sharp are their edges? What are the general shapes of C1R and C2R? Do they consist of solidly precessing ellipses like some Saturn's or Uranus' ringlets? Do they have more complex proper modes with higher azimuthal wave numbers? Are there other fainter rings around Chariklo? What is the shape of the object itself and its role for the ring dynamics? Based on new results, what can we learn about their origin and evolution, which remains elusive (Sicardy et al. 2016)? This study is made in a context where material has also been detected around the second largest Centaur, Chiron (again using stellar occultations). The nature of this material is still debated and it could be interpreted as a ring system (Ortiz et al. 2015) or a dust shell associated with Chiron's cometary activity (Ruprecht et al.